Panel structure



FIG. 1 is a perspective view of the front of a panel structure embodying my design;

FIG. 2 is a perspective view of the back of the panel structure shown in FIG. 1; and

FIG. 3 is a fragmentary plan view showing the upper right corner of the panel structure shown in FIGS. 1 and 2. 

The ornamental design for a panel structure, substantially as shown. 